linux-kernel - Re: [PATCH v4 2/6] tpm: remove definition of TPM2_ACTIVE_PCR

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Date:   Thu, 8 Nov 2018 16:03:18 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     zohar@...ux.ibm.com, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v4 2/6] tpm: remove definition of TPM2_ACTIVE_PCR_BANKS

On Thu, Nov 08, 2018 at 04:02:08PM +0200, Jarkko Sakkinen wrote:
> On Tue, Nov 06, 2018 at 04:01:55PM +0100, Roberto Sassu wrote:
> > tcg_efi_specid_event and tcg_pcr_event2 declaration contains static arrays
> > for a list of hash algorithms used for event logs and event log digests.
> > However, according to TCG EFI Protocol Specification, these arrays have
> > variable sizes and are not suitable for parsing events with type casting.
> > 
> > Since declaring static arrays with hard-coded sizes does not help to parse
> > data after these arrays, this patch removes the declaration of
> > TPM2_ACTIVE_PCR_BANKS and sets the size of the arrays above to zero.
> > 
> > Fixes: 4d23cc323cdb ("tpm: add securityfs support for TPM 2.0 firmware
> > event log")
> > 
> > Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> > ---
> >  include/linux/tpm_eventlog.h | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> > 
> > diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
> > index 20d9da77fc11..3d5d162f09cc 100644
> > --- a/include/linux/tpm_eventlog.h
> > +++ b/include/linux/tpm_eventlog.h
> > @@ -8,7 +8,6 @@
> >  #define TCG_EVENT_NAME_LEN_MAX	255
> >  #define MAX_TEXT_EVENT		1000	/* Max event string length */
> >  #define ACPI_TCPA_SIG		"TCPA"	/* 0x41504354 /'TCPA' */
> > -#define TPM2_ACTIVE_PCR_BANKS	3
> >  
> >  #define EFI_TCG2_EVENT_LOG_FORMAT_TCG_1_2 0x1
> >  #define EFI_TCG2_EVENT_LOG_FORMAT_TCG_2   0x2
> > @@ -90,7 +89,7 @@ struct tcg_efi_specid_event {
> >  	u8 spec_errata;
> >  	u8 uintnsize;
> >  	u32 num_algs;
> > -	struct tcg_efi_specid_event_algs digest_sizes[TPM2_ACTIVE_PCR_BANKS];
> > +	struct tcg_efi_specid_event_algs digest_sizes[0];
> >  	u8 vendor_info_size;
> >  	u8 vendor_info[0];
> >  } __packed;
> > @@ -117,7 +116,7 @@ struct tcg_pcr_event2 {
> >  	u32 pcr_idx;
> >  	u32 event_type;
> >  	u32 count;
> > -	struct tpm2_digest digests[TPM2_ACTIVE_PCR_BANKS];
> > +	struct tpm2_digest digests[0];
> >  	struct tcg_event_field event;
> 
> Last two fields make sense at least without comment as they overlap.

i.e. would be semantically equal to

union {
	struct tpm2_digest digests[0];
	struct tcg_event_field event;
};

/Jarkko